First of all we established the rat colitis model induced by sulufonic acid (TNBS) enema. We investigated whether n-butyric acid that was produced from fermentation of dietary fiber in colon would have preventive effects to the rat-colitis model induced by TNBS enema. For clarifying that effect we designed the experiment that one group of rats received n-butyric acid enema once an everyday for a week before TNBS enema and another group of rats received saline-enema once an everyday for a week before TNBS enema. And two days after TNBS enema we compared the area of ulcer and pathological findings of colitis between two groups of rats. The enema of n-butyric acid, at concentration of 30mg/ml, significantly reduced the area of ulcer and scores of pathological findings, inflammatory cell's infiltration, submucosal edema and bleeding induced by TNBS enema compared with saline-enema. Next for revealing of the mechanism of anti-inflammatory effect of n-butyric acid, we studied the the contents of myeloperoxidase activity (MPO) and interleukin-1B (IL-1B) of colitis. The enema of nbutyric acid also significantly reduced the contents of MPO and L-1B of homogenized colon tissue compared with that of saline.Furthermore, we studied whether n-butyric acid would have the effect of inducing mucine production by mucosal cells. We revealed the effect of n-butyric acid inducing mucine production by rat colon mucosal cells.This study suggests that taking in dietary fiber could prevent the deteriorate of ulcerative colitis.